Loaded antenna



w. R. KOCH LOADED ANTENNA Feb. 14, 1939.

Filed Feb. 20, 1937 Gttorneg Patented Feb. 14, 1939 UNITED STATES LOADED ANTENNA Winfield R. Koch, Merchantville, lN. J., assigner toRadio Corporation of America, a corporation of Delaware Application February 20, 1937, Serial No. 126,750

2 Claims.

My invention relates to transmitting antennas,`

and more specifically to improved means for loading a transmittingv antenna to thereby increase its effective*heightorservice area. I am aware that it has Vbeen* proposed' toincrease the effective height of a transmitting antenna by means vof a capacity section vlocated at the top of the antenna, which is coupled through a loading reactor to the lowersection of the antenna. It has also been proposed to increase the elfective height or service area of a transmitting antenna by dividing the antenna into an upper section and a lower section, which are joined by a loading inductor.

' There is a practical limit to the amount of loading which may be applied to either the capacity top antennas orthe sectionalized antennas. The amount of loading inductance which is required depends upon the actual height of a givenl an- 90 tenne. and the wave length at which the antenna is to be operated. As the antenna is made shorter, more and more loading reactance is required. Since this reactance must carry the entire'current which is owing into the upper section of the antenna, it becomes necessary to designv the loading inductor with a very large cross-sectional conductor. The physical limitationssurrounding the design of such an inductor p-laces a limit which is largely'determined by the amount of $0- permissible power loss.

It should be understood that the government licensing of radio transmitters is based upon the power actually applied to the antenna. If a sectionalized antenna is employed which has large resistive losses due to the loading inductor, such losses cannot be overcome by applying larger power inputs, if the transmitter has already applied the authorized power input.

As the losses in the sectionalized antenna increase, the service area decreases. Thus, one of the purposes of sectionalizing an antenna is defeated by the losses incurred in attempting to apply too large a loading inductor which is accompanied by excessive power losses.

My invention contemplates substantially reducing the power lost in a concentrated inductor with the resulting benets. One of the objects of my invention is to provide means for substantially 50 increasing the amount of loading inductance without greatly increasing the power losses.

Another object of my invention is to provide reactive loading means in a sectionalized antenna which will reduce the power losses.

A further object of my invention is to substi- (Cl. Z50-33) tute a concentric line loading reactor for the conventional concentrated inductor.

A further object of my invention is to provide a concentric line which has the characteristics of a radio frequency choke coil, for the lighting 5 circuit which is generally used to energize signal lights on the top of an antenna structure.

My invention may be best understood by referring to the accompanying drawing, in which Figure 1 represents an elevational View, partly 10 in section, of one embodiment of my invention,

Figure 2 represents a concentric line reactor applied to a sectionalized antenna and a lighting line in accordance with my invention, and

Figure 3 represents a sectional view showing a 15 portion of an antenna tower and a concentric line.

In Fig. 1, an antenna comprising a structural steel tower I is insulated from ground by insulators 3. At a point substantially two-thirds the distance from the base to the top of the antenna, insulators 5 are inserted tothereby separate the tower into two sections. The reference number 'l is applied tothe upper section. In some installations, a capacitor 9 may be added to the top 25 of the antenna and insulated therefrom by insulators Il. v

The lower section of the antenna is coupled t0 the uppersection 'l of the antenna by a concentric line I3. This concentric line is comprised 3o of an inner element of Apreferably cylindrical form l5, and an outer element vI'l which is also preferably o-f cylindrical form and is concentrically arranged with respect to the inner member. The inner member is connected to one section of the tower, and the outer member is connected to the other section. In the instant case, the inner member is conductively secured to the lower section of the tower and the outer member is conductively fastened to the upper section of the 40 tower. It should be understood that this connection may be reversed.

The upper ends of both the inner and the outer conductors are connected together at a point Which will determine the length of concentric line which will offer a suitable reactance to currents of the desired frequency. One method of adjusting the concentric line to the desired reactance is to have the short-circuiting device which couples the ends of the concentric elements adjustable. Another method of determining the proper reactance is to iirst connect a calibrated inductor between the upper and lower sections and, having measured the inductance, a concentric line of like value is substituted therefor.

the inner conductor.

In certain installations, the capacitive top 9 may be used in place of the sectionalized loading reactor I3. In this event, a concentric line I9, having the characteristics of the concentric line I3 previously described, is connected between the capacitive top 9 and the adjacent insulated section of antenna 'I. When only the capacitive top is used, the tower I would not be insulated at the two-thirds point as previously described. In some installations, both the sectionalized antenna and the capacitive topl may be employed. Y

In Fig. 2, a sectionalized antenna without th capacitive top has been equipped with a lighting line 2l which conveys power to the signal lamp 23. The lighting wires are installed Within the tower. To avoid undesired reaction between the high frequency radio currents and the lighting line currents, a concentric line 25 is connected between the base of the antenna, which is insulated at 21, and ground. The lighting or power wires 2I extend through the concentric line 25. By adjusting the length of the line 25 to onequarter of the wave length to be radiated from the antenna, the lighting line is made to assume the characteristics of a radio frequency choke. The radio frequency choke characteristics are determined by the close coupling of the lighting line and the quarter wave concentric line.

Inasmuch as the concentric line reactors I3, I9 and 29 must carry large amounts of current at high voltage, I prefer to use good electrical conductors of large cross-section which are well separated to thereby avoid corona and resistance losses. By employing concentric lines of this type, I have found that their figure of merit, which is the ratio of reactance to resistance, may be increased many times. The impedance of the line is determined by the equation:

Z: 138 logmg where D equals the inside diameter of the outer conductor and d equals the outside diameter of The reactance may be determined from the equation:

X Z0 tan Zir where L=length of line and k=wave length.

By Way of example, the figure of merit of a well designed concentrated helical inductor at broadcastfrequencies is generally of the order of to 200. I have been able to increase the ratio of reactance to resistance in a concentric line of similar reactance at broadcast frequency to several thousand. Since this increase is of the order of ten times, it will be apparent that I can greatly reduce the losses when a concentric line is used in place of the conventional loading reactor, or I can use a much shorter antenna tower and greatly increase the amount of inductive loading without correspondingly increasing the losses as would be the case in a conventional installation.

I claim as my invention:

1. An antenna including an upper section, a lower section, means for insulating said sections from each other, means for insulating said lower section from ground, a concentric line connecting said sections and having an effective length which offers inductive reactance to currents of the frequency at which said antenna is operated, a concentric line connecting said lower section and ground, a signal light mounted on said antenna, and` a power line positioned within said second mentioned concentric line and connected to said signal light, said power line and second mentioned concentric line having a length which substantially prevents radio frequency currents from entering said power line.

2. An antenna including an upper section, a lower section, means for insulating said sections from each other, means for insulating said lower section from ground, a concentric line connecting said sections, having an effective length which offers inductive reactance to currents of the frequency at which said antenna is operated, and wherein the ratioof said reactance to the resistance of said line is of the order of one thousand, a concentric line connecting said lower section and ground, a signal light mounted on said antenna, and a power line positioned within said second mentioned concentric line and connected to said signal light, said power line and second mentioned concentric line having effective lengths substantially equal to a quarter wave length of the currents impressed on said antenna whereby said antenna is grounded for currents other than said impressed currents and insulated with respect to said impressed currents, and said impressed currents are substantially prevented from entering said power line.

WINFIELD R. KOCH. 

